Extensive ab initio SCF and CI calculations have been performed on the valence and Rydberg excited states of pyrazine, as well as the low-lying cationic states. The results are used to interpret the ultraviolet and photoelectron spectra. Simple models for describing the $n\pi^{*}$ and lone pair cation states are developed. The possibility of having an electric-dipole forbidden$^{1}$ $n\pi^{*}$ state nearly degenerate with the lowest observed$^{1}$ $n\pi^{*}$ state is considered.